The primary objective of this study is to assess the relationship between exposure to phenoxy herbicides and the risk of spontaneous abortion in a cohort of Ontario farm families. Although there have been general investigations which have suggested that these chemicals are carcinogenic in humans and embryotoxic and teratogenic in animals, this study will be the first to examine this relationship in a farm population, in which a large number of reproductive-age women are potentially exposed. Two sub-cohorts of farm operations that vary in potential exposure to phenoxy herbicides will be identified based on the Census of Agriculture. Farming couples will be mailed questionnaires which will obtain information on agricultural chemicals used, reproductive history activities on the farm, and other potential risk factors for spontaneous abortion. Multiple logistic regression will be used to assess the effect of phenoxy herbicide exposure on spontaneous abortion, controlling for confounding factors. The wide usage of these chemicals, both in agricultural and residential settings (especially 2,4-D), the suggestive evidence of toxicity from the results of epidemiological and toxicological studies, and the profound consequences of adverse reproductive out!comes both to the individuals and the public, suggest that this topic warrants further study.